The present invention relates to a process for preparing a scale deposition preventing agent, and more particularly to a process for preparing a scale deposition preventing agent of a quinone-amine compound having a molecular weight of not less than 3000, which comprises subjecting an aromatic quinone and an aromatic diamine to addition reaction in a solvent medium having a solubility parameter of 8.5 to 24.0, and converting the addition product into a high molecular weight compound by adding an oxidizing agent or conducting anodic oxidation.
The scale deposition preventing agent according to the present invention is used in a process for emulsion-polymerizing an acrylate or a methacrylate monomer alone, a mixture thereof or a mixture of an acrylate or a methacrylate monomer as a main component and other copolymerizable monomers, wherein the amount of the acrylate monomer, methacrylate monomer or mixture thereof becomes not less than 60% by weight of the monomer mixture in the course of the emulsion polymerization by previously applying to an inner surface of a polymerization vessel and surfaces of attached instruments within the vessel.
An emulsion polymerization using an acrylic or a methacrylic acid ester (hereinafter referred to as "(meth)acrylate") monomer is popularly applied to a process for preparing an acrylonitrile-butadiene-styrene copolymer (ABS) or a methyl methacrylate-butadiene-styrene copolymer (MBS). In such a process, the polymerization is carried out in a manner of graft-polymerization using a butadiene rubber latex. As a result of the polymerization, since the formed polymer scale is adhesive, the scale is hardly removed from an inner surface of a polymerization vessel.
The deposition of the polymer scale is assumed to occur in the following manner. The (meth)acrylate monomers are dissolved in water, and then polymerized in water, which makes a latex unstable. In addition, since the (meth)acrylate monomers are hydrolyzed to acidify the polymerization system weakly, coagulation of the latex is promoted. For preventing the latex from the coagulation, a proper emulsifier is selected. It is very difficult, however, to carry out the polymerization in a stable state of the latex, because the quality of the produced polymer becomes degraded by the increase of the amount of the emulsifier. Therefore the partial coagulation of the latex cannot be avoided.
The coagulated latex is dissolved in the (meth)acrylate monomers to increase in stickness. The sticky coagulated latex is adhered on surfaces of various parts in a polymerization vessel, and then the (meth)acrylate monomers contained in the latex are polymerized thereon to form a tough polymer scale deposition.
This causes many defects such as decrease in heat transfer efficiency through the inner wall of the vessel, decrease in yield, deterioration of products due to the admixing of the peeled scales, and reduction in operating rate of the vessel due to labors and time required for removing the scales from the surface.
In order to prevent the scale deposition, there was proposed a process wherein, in a process for emulsion-polymerizing an acrylate or a methacrylate monomer alone, a mixture thereof or a mixture of an acrylate or a methacrylate monomer as a main component and other copolymerizable monomers in the presence of water, an emulsifier and a polymerization initiator soluble in water or the monomers, wherein the amount of the acrylate monomer, methacrylate monomer or mixture thereof becomes not less than 60% by weight of the monomer mixture in the course of the emulsion polymerization; the improvement which comprises carring out the emulsion polymerization in a polymerization vessel having a film on an inner surface thereof and on surfaces of attached instruments within the vessel, the film being formed by applying a solution of an aromatic quinone-amine compound having an average molecular weight of not less than 3,000 in an organic solvent, the quinone-amine compound being prepared by subjecting an aromatic diamine and an aromatic quinone to addition reaction in an organic solvent medium having a solubility parameter of 9.0 to 12.2, in U.S. Pat. No. 4,517,344 by the present inventor.
However, the process described in U.S. Pat. No. 4,517,344 has defects that the preparation rate of a quinone-amine compound is very slow, that is, a long time as about 30 days is required until the precipitation of the desired product begins, and the yield is very low, i.e. from 2 to 23%.
It is an object of the present invention to provide a process for preparing a scale deposition preventing agent solving the above-mentioned defects.
This and other objects of the present invention will becomes apparent from the description hereafter.